Abroad irradiation method is an irradiation method which has been most broadly used in a particle beam irradiation apparatus used for medical care such as a cancer treatment, etc. and for researches. The broad irradiation method is a method of spreading a charged particle beam by using a scattering member and a wobbler electromagnet and reducing irradiation to places other than a diseased site by using a collimator or a bolus.
In addition to the broad irradiation method for irradiating an irradiation subject area at a stroke, a scanning irradiation method for irradiating a diseased site as an irradiation subject with a charged particle beam every small area while scanning the charged particle beam, such as spot scanning or raster scanning has been proposed (for example, non-patent document 1). There have been also proposed a technique in which a conventional particle beam irradiation apparatus for performing scanning irradiation disclosed in the non-patent document 1 is further modified so that a scanning electromagnet is disposed at the upstream side of a final bending electromagnet, thereby remarkably reducing the radius of a gantry (patent document 1) and a technique in which the scanning electromagnet can be omitted (patent document 2). Furthermore, means for correcting a deflection scanning position displacement in a charged particle bean scanning apparatus used to irradiate a beam onto a sample has been proposed although it is not a particle beam irradiation apparatus for medical care or for researches (patent document 3).
It is general in the scanning irradiation method that a part for preventing irradiation to normal tissues other than a diseased site such as a collimator or a bolus used in the broad irradiation method is not provided, and thus higher beam position precision than the broad irradiation method is required. As described above, a device for compensating the beam position precision has been hardly disclosed although the scanning irradiation method requires the higher beam position precision than the broad irradiation method.
Furthermore, when a charged particle beam of proton, carbon ion or the like is incident into substance such as the body or the like, it travels till the specific depth (called as a range) corresponding to the energy of the charged particle beam in the substance, a peak at which the maximum energy is applied from the charged particle beam to the substance exists in the neighborhood of the terminal of the range (called as “Bragg peak”), and the charged particle beam has a characteristic that the Bragg peak thereof has a shaper depth dose distribution as compared with other radiation rays such as X-ray, etc. The particle beam irradiation apparatus suppresses the charged particle beam from affecting normal tissues by utilizing this characteristic, whereby the dose is concentrically irradiated onto the diseased site. From this viewpoint, in a scanning particle beam irradiation apparatus or treatment plan apparatus for performing spot scanning or raster scanning, control amounts for scanning means and an accelerator have been hitherto calculated on the assumption that the in-body depth direction (Z direction) of the desired irradiation position and the X-direction and Y-direction perpendicular to the Z direction can be separately controlled by adjusting the energy of the charged particle beam and controlling the scanning means such as the scanning electromagnet or the like, respectively.